Path: news.daimi.aau.dk!jco
From: jco@daimi.aau.dk (Jens Cornelius Olsen)
Newsgroups: comp.lang.beta
Subject: Re: Recursive, double INNER
Date: 9 Feb 1995 17:56:29 GMT
Organization: DAIMI, Computer Science Dept. at Aarhus University
Lines: 80
Message-ID: <3hdl0d$c2l@belfort.daimi.aau.dk>
References: <ALFH.95Feb6204201@byleist.ifi.uio.no>
NNTP-Posting-Host: rennes.daimi.aau.dk

Thus spake alfh@byleist.ifi.uio.no (Alf-Ivar Holm):

> ...
>It works, but there are one more problem, if you make a sub pattern,
>e.g. forAllDingbats, the forAllThings super pattern is still called.

>Next thought:  Make a virtual function, 'callMe', which is bound to
>the current (sub)pattern:
>	
>	forAllThings:
>	(# 
>	   before:< object;
>	   after:< object;
>	   callMe:< forAllThings;
>	do
>	   before;
>	   ... &callMe ...
>	   after;
>	#);

Nice try !

> ...
>Finally, I would usually use forAllThings directly, not making a
>specific sub pattern:
>	
>	do
>           ...
>           &forAllThings
>	   (# 
>	      before::< (# ... #);
>	      after::< (# ... #);
>	      callMe::< (* What am I supposed to put here? *) ;
>	   #);
>	     
>My problem is that I don't manage to bind callMe to that specific
>instance.  

>What am I missing?  Some minor syntactic detail?  Some major
>fundamental issues about programming or BETA?  A course about
>rewriting recursive algorithms to non-recursive?

>	Affi

My solution would be to use THIS() and pattern variables.  In a *true*
recursive version this amounts to something like this

   forAllThings:
     (#
        before:< object;
        after:< object;
        callMe: ##forAllThings;
     do before;
        this(forAllThings)##-> callMe##; &callMe;
        after;
     #);

Where the pattern variable is used to duplicate the subpattern of forAllThings
in question.  From previous email correspondance with Ole Lehrmann Madsen, one
of the designers of BETA, I know that it was (or is) considered to include
a shorter version of the two statements involving callMe in the syntax:

                 &(this(forAllThings)##)

but for now we are forced to use the callMe variable.

\Jens
______________________________________________________________________________

Jens Cornelius Olsen,                                 Email: jco@daimi.aau.dk
Student at Aarhus University,
Office: B18/B1.13,                                    phone: +45 89 42 33 48
Home: Skelagervej 181,                                phone: +45 86 10 91 65
      8200 Aarhus N,
      Denmark, Europe.
______________________________________________________________________________